Condition responsive control device



June 1, 1943. H. F. PETERSON qonnnrou RESPONSIVE CONTROL DEVICE Filed April 3, 1942 Q/enzg erd/ham pezjzsav view Patented June 1, 1943 'U-NITED STATES PATENT OFFICE CONDITION RESPONSIVE CONTROL DEVICE Henry Ferdinand Peterson, Rockford, Ill. Application April 3, 1942, Serial No. 437,558

, 3 Claims. (Cl. 200-137) This invention relates to condition responsive control devices such as humidos'tats, and the primary object is to construct such a device simply by the addition of a condition responsive element to a switch unit of standard construction.

A more detailed object is to utilize the casing of a standard self-contained sensitive switch unit as a mounting for a. condition responsive element extending partially around the casing and moving the switch actuator of the unit as the element expands or contracts with condition changes. v v

The invention also resides in the novel manner of mounting the condition responsive element and of providing for adjustment of the instrument control point.

Other objects and advantages of the invention control device is built around an extremely sen-.

sitive standard switch unit 5 manufactured by the Micro-Switch Corporation of Freeport, Illinois. The unit comprises generally a rigid synthetic resin casing 6 of box-like iorm having therein a flexible resilient metal arm 1 one end 01' which is anchored by a screw 8 to a ledge 9.

The tree end of the arm carries a contact Hi 00- acting with a stationary contact H to form a switch l2. Spring arms ll integral with the free end of the arm I are bowed and project reversely with their free ends seated in notches I! in the edge of a plate IS. The arms I! produce an over-center or detent action that causes the arm 1 to move the contact l0 between the contact H and a step I6 with a snap action. A button l1 bearing against the arm I near its anchored end carries a pin it projecting through a hole in one wall of the casing. Movement of the pin of about .001 of an inch is sufllcient to open or close the switch.

The present invention contemplates utilizing Q the casing 6 as a mounting for a sensitive con dition responsive element disposed externally of the casing and operable to actuate the pin II. The element is of a type which expands and contracts with opposite changes of an ambient condition and comprises a band or ribbon l9 encircling the casing 8 lengthwise in the form shown in Figs. 1 and 2 with its ends united by adhesive or by a suitable clip 20 so as to form a complete loop. To minimize friction, the band may be extended around rollers l9 which hold the band spaced from the sides of the casing and are mounted on the latter in a manner to be described later. One side of the loop is spaced from the casing and bears against a cross-bar 2| on the pin I8 so as to press the latter inwardly and open the switch I2 as the loop contracts. If desired, the cross-bar may carry an anti-triction roller. The loop permits outward movement of the pin over the bias of the spring arms l3 as the loop expands, this resulting in closure of the switch.

It will be observed that the projecting portion 01' the pin it constitutes the altitude of two right triangles each having a hypotenuse formed by the length of the band between the cross-bar and one corner of the casing. Thus a very small change in the length of this hypotenuse will produce a comparatively large change in the altitude which latter change is represented by the switch actuating motion of the pin l8. In this. way, the elongation or contraction of the band is magnified many times and applied to the switch. This coupled with the small motion that is required to actuate the switch makes the instrument very sensitive.

Where the instrument is to respond to changes in relative humidity, the band may be composed of a series of strands of hair or of any other material such as so-called Cellophane which will absorb moisture from the air and expand proin Fig. 1, plates 22 lying against one side of the casing 6 have flanges 23 disposed adjacent the ends of the casing and carrying the rollers IB that deflne'the ends of the band loop. By varying the spacing of the plates, the tension on the band for a given ambient condition may be varied to produce the desired control point of the instrument. Screws 24 projecting through slots 25 and threading into the casing serve to clamp the plates into their adjusted positions.

In the modification shown in Fig. 3, the band l9 extends only partially around the casing i having the ends anchored to the casing ends by clamps 24. Adjustment of the control point may be effected by shifting a plate 25 longitudinally of the casing. This plate has an arm 26 disposed externally of and bearing against the unsupported side of the band l9 so as to vary the tension on the latter. The plate position is maintained by a clamping screw 21 projecting through a slot 28 and threading into the casing in this instance.

The control instrument thus provided is simple in construction and very inexpensixe because it utilizes a standard switch unit and in addition employs the casing of this unit as a mounting for the condition responsive element anti the parts of the adjusting mechanism. It will be observed that the members it and which transmit the transverse movement of the condition responsive element it to the switch actuating member "at incorporate a bearing connection which permits the member to move ahead of the condition responsive element so that the switch member may be moved from one position to another with the desired snap action.

I claim as my invention:

1. A condition responsive instrument having, in combination, a switch, a casing enclosing said switch, a member projecting through a wall of said casing and movable in and out to actuate the switch, a flexible element supported by said casing and stretched around said member to move the latter in and out during contraction and expansion of the element in. a direction transversely of the direction of movement of said member, and means mounted on sairi caa= ing and selectively adjustable to vary the tension on said element and thereby change the control in combination, a switch unit comprising a rigid casing and a switch-actuating member projecting from one wallet the casing and movable back and forth therethrough, and a flexible element stretched'along said wall with its opposite ends anchored to saizi casing and an intermediate portion engaging said member to effect movement oi the latter in and out 05; said casing by elonga tion and contraction oi salri element longitudinally of said wall, said element being expansible and contractible with ambient condition changes.

3. A condition responsive instrument having, in combination, a rigid casing, a switch unit within said casing having a member movable between switch closed to switch open positions with a snap action, said member normally tending to move to one of said positions, a flexible element extending along a wall of said casing and secured at opposite ends to the casing, said element being expansible and. contractible longitudinally with ambient condition changes whereby to cause transverse movement oi an intermediate portion of the element toward and away from the wall, and means including a bearing connection for transmitting said transverse movement in one direction to initiate said snap acting movement of the member, said bearing connection permitting of movement of said member ahead of the element.

HENRY raaommn PON. 

